THE B REGIONAL DUST STORM IN THE NEW NASA AMES MARS GCM.
C.M.L. Batterson, Bay Area Environmental Research Institute, Moffett Field, CA, USA (courtney.m.batterson@nasa.gov),
M.A.Kahre, NASA Ames Research Center, Moffett Field, CA, USA, A.F.C. Bridger, Department of Meteorology, San
Jose State University, San Jose, CA, USA, R.J.Wilson, NASA Ames Research Center, Moffett Field, CA, USA,
R.A.Urata, Bay Area Environmental Research Institute, Moffett Field, CA, USA.

Introduction
The Thermal Emission Spectrometer (TES) and the
Mars Climate Sounder (MCS) instruments have been observing global dust and temperature on Mars twice daily
for a combined ∼12 Mars Years (MYs). Analysis of
these data by [5] reveal three highly repeatable, regional
scale dust events occurring annually during years lacking a global dust storm (GDS). Named the "A," "B," and
"C" storms in seasonal order, these recurring dust storms
develop in the southern hemisphere of Mars during the
perihelion season (Ls =180°–360°) when Mars is closest
to the sun and the southern hemisphere experiences summer [5]. The "A" and "C" storms occur in the southern
midlatitudes where they amplify the Hadley circulation
causing dynamical warming in the northern hemisphere.
In contrast, the "B" storm (hereafter, B storm) and its effects are entirely confined to the south pole [5]. All
three storms are large enough to inject dust above the
boundary layer [8]. As a result, the annually-recurring
regional storms produce significant temperature perturbations in the middle atmosphere, raising zonal mean 50
Pa ( 25 km) temperatures above 200 K (Figure 1) [5].
In this work, we seek to identify the mechanisms
responsible for lofting dust into the middle atmosphere
during the B storm by simulating the storm with the new
NASA Ames Mars Global Climate Model (MGCM).
We find that the simulated B storm is driven by a series of dust plumes that form in the high southern latitudes during southern summer solstice. We also find that
radiative-dynamic feedbacks between airborne dust and
incoming shortwave radiation are crucial for the pluming
mechanism.
Methods
We simulate the B storm using the new NASA Ames
MGCM with the finite-volume dynamical core and cubedsphere grid developed by NOAA/GFDL. Model topography is derived from high-resolution (1/16°) Mars Orbiter Laser Altimeter (MOLA) retrievals while surface
thermal inertia and albedo are derived from TES observations [7, 10]. The seasonal growth and recession of
the north and south polar ice caps maintain a surface
energy balance that is dependent, in part, on the albedo
prescribed to each. We use the nominal albedos of 0.7
and 0.51 for the north and south polar caps, respectively, which we find to produce a good fit to the Viking
Lander-observed surface pressure cycle.

Figure 1: Observed zonal mean daytime (3 PM) 50 Pa temperatures (top) and dust mixing ratios (bottom) for Ls = 180°–
360° in MY32. The red contour is the 200 K isotherm and the
dashed line marks the northernmost edge of the receding CO2
ice cap.

Water ice cloud microphysics are excluded from our
simulations, but the radiative properties of dust and
gaseous CO2 are included in a 2-stream RT scheme
[3, 9]. Gaseous opacities for CO2 are calculated from
correlated-k tables and Rayleigh scattering for CO2 is
computed directly. The optical properties of dust depend on the particle size distribution of dust in the atmosphere. In the MGCM, dust mass and number mixing
ratios are carried as tracers and used to compute the
temporally and spatially-evolving effective particle size
distribution. The optical properties of the dust are calculated from Mie theory and then weighted according to
the size distribution of the aerosol [3].
Dust aerosols are a major source of radiative forcing on Mars and their effects are largely dependent on
the size distribution of dust in the atmosphere [11]. In
the MGCM, the size distribution of the lifted dust particles is determined by a user-assigned effective radius
(ref f ), and airborne dust is then allowed to evolve, radi-

modeling the B storm
ate, be transported by resolved winds, and sediment out
due to gravity [3]. The MGCM dust lifting scheme is
constrained by a set of daily global dust column opacity maps from [6], which are used to indicate when and
where dust should be injected into the lowest model layer
[3, 11].
The MGCM was run at ∼1°x1° (∼60x60 km) horizontal resolution with a terrain-following, 30-layer hybrid σ -pressure vertical coordinate featuring a ∼6 m
vertical resolution near the surface and ∼10 km resolution near the top (∼90 km). The MY31 daily global
dust opacity maps were used to inform the dust lifting
scheme, and the lifted particle effective radius was set
to ref f =3 µm , which was the same value used to reproduce the MY34 GDS in the MGCM and which we
find reasonably reproduces the observed B storm [6, 1].
The MGCM was run for two years, and output from the
second half (Ls =180°–360°) of the second year was
analyzed in this study.
Results
The behavior of the simulated B storm closely follows that of the observed B storm. The simulated B
storm occurs poleward of 60° S during southern summer
solstice as observed, and its growth phase is marked by
a rapid increase in middle atmospheric temperatures and
dust concentrations. Figure 2 shows that 50 Pa B storm
temperatures maximize at ∼15 K above normal just before solstice and exceed 200 K for ∼10° of Ls around
solstice. Corresponding dust mixing ratios exceed 4 ppm
during the same period, maximizing near ∼6 ppm. After solstice, the simulated B storm slowly decays as dust
falls out of suspension allowing temperatures to return
to normal ∼15° of Ls after the storm’s peak. Overall,
the simulated B storm is shorter-lived (and somewhat
weaker) than observed, but it nonetheless meets the criteria for a B storm event: 50 Pa temperatures exceed
200 K, 50 Pa dust exceed 4 ppm, there is no northern
hemisphere response, and the storm maximizes around
southern summer solstice (Ls =270°) [5].
The simulated global mean thermal and dynamical
structure of the southern summer atmosphere are shown
in Figure 3. Simulated temperatures reflect a large nearsurface thermal gradient with a maximum of just over
240 K at the south pole and a minimum of 140–150 K
at the north pole. There is a northward-tilting column
of warm air over the winter pole and a steep thermal
gradient through the column over the south pole. The
simulated atmosphere is somewhat cooler than observed
in parts of the upper atmosphere, however, temperatures
in the lower and middle atmosphere are comparable to
the observed environment. The zonal mean overturning
circulation is dominated by a cross-equatorial Hadley
cell with a rising branch located around 40° S and a sinking branch over ∼60° N. The southern summer Hadley
cell lofts dust tens of kilometers and disperses it globally [4]. However, the B storm is located tens of degrees

Figure 2: As in Figure 1 but for simulated temperatures and
dust mixing ratios.

in latitude south of the Hadley cell precluding it from
facilitating dust lofting in the B storm. In fact, the zonal
mean circulation indicates air is predominantly sinking
over the south pole during the B storm. The thermallydirect polar cell (blue) in Figure 3 shows air is ascending over ∼75° S, traveling southward at ∼50 Pa, and
descending over the south pole where the B storm is
occurring. Thus, the mean overturning circulation provides little evidence for dust lofting during the B storm,
which suggests the primary dust lofting mechanism is
likely a process local to the south pole.
The MGCM shows the B storm is driven by repetitive dust plumes which inject dust above the boundary
layer where dust radiative heating enhances convection
and thereby maintains dust aloft in the middle atmosphere. One such dust plume is illustrated in Figure
4, which shows dust mixing ratio (shaded), shortwave
(SW) heating rate (contoured), and net vertical velocities (combined vertical wind and sedimentation rate;
arrows). Mixing ratios within the dust plumes are typically 6–8 ppm and can be as high as 14 ppm at the
core of the most opaque plumes. Most of the plumes
form in the eastern hemisphere, specifically around 100°
E longitude, and travel westward for half a day before
producing a detached dust layer. Detached layers have
mixing ratios comparable to the dust plumes (6–8 ppm),
although mixing ratios within the detached layers rarely
exceed 10 ppm. Detached layers travel west for ∼12
hours before re-entering the eastern hemisphere where a
new dust plume is typically developing.
The sizes of the dust plumes are largely consistent

modeling the B storm

Figure 3: Zonal mean temperatures (color-filled) and mass
streamfunction (MSF; contoured) during southern summer
(Ls =255°–285°). From left to right, the MSF field shows a
thermally-direct polar cell (blue) south of 75° S, a thermallyindirect midlatitude cell (orange) between 60°–75° S, a
thermally-direct Hadley cell (blue) between 40°–60° S, the
Hadley cell (orange), and a thermally-indirect polar cell (blue)
poleward of 65° N.

throughout the duration of the B storm, with the exception that the plumes that form on the 2–3 days around
solstice (Ls =270°) are the largest. The majority of
B storm dust plumes are 3–4 scale heights tall, which
places the uppermost part of the plume at around ∼10
Pa. However, the largest plumes can be up to 5 scale
heights tall, around ∼3 Pa. The width of the dust plumes
varies between ∼25°–100° in longitude, but most are
∼50° longitude wide. The detached dust layers produced by these plumes are located between 5–10 Pa and
are no more than ∼25° of longitude wide. They tend to
elongate over time as dust falls out of suspension.
The concentration of dust within a plume is highly
correlated with the SW heating rate, especially above
the boundary layer (∼1 scale height). SW heating rates
are ∼30–45 K/day for mixing ratios between ∼6–8 ppm,
and over ∼60 K/day for mixing ratios greater than ∼14
ppm. Positive (upward) net vertical velocities (with sedimentation rates subtracted) are ∼10–20 cm s−1 where
SW heating rates >45 K/day (and, accordingly, mixing
ratios >8 ppm), and can exceed ∼40 cm s−1 just above
dust plumes and detached layers on the dayside of the
planet.
The simulation suggests that the radiative-dynamic
feedbacks caused by the presence of dust above the
boundary layer are crucial to the B storm. In fact, in
a simulation with radiatively inert transported dust the
B storm does not occur. Figure 5 emphasises this point,
showing the dust, vertical wind, and SW heating rate
at Ls =270.19° as in Figure 4 but for the simulation
in which transported dust is radiatively inert. There is
no dust above the boundary layer in Figure 5, and in
the absence of dust radiative heating, SW heating rates
and positive net vertical velocities maximize around the
longitude of local noon. However, even the strongest
updrafts in this scenario are unable to loft dust above

Figure 4: Simulated dust mixing ratio cross-section at 75 °S,
Ls =270.19°. Dust mixing ratio is shaded, shortwave heating
rate is contoured, vertical velocities (with dust sedimentation
rates subtracted) are indicated by the arrows. Local noon is at
±180°.

the boundary layer, highlighting the importance of the
dust radiative-dynamic feedback in producing the dust
plumes.

Figure 5: As in Figure 4 but for the radiatively inert dust case.

Conclusions and Future Work
The MGCM reproduces the B storm with middleatmospheric temperatures and dust concentrations commensurate with observations. The simulated B storm is
weaker than observed but has most of the characteristics
of the observed B storms: zonal mean 50 Pa temperatures exceeding 200 K, zonal mean 50 Pa dust mixing
ratios exceeding 4 ppm, peak intensity occurring at solstice (Ls =270°), and a short growth period followed by
a long decay period.
The MGCM predicts that the B storm is comprised
of westward-propagating dust plumes that form primarily in the eastern hemisphere and often produce detached
dust layers. These dust plumes are self-sustaining: air-

REFERENCES

borne dust absorbs and re-radiates heat, enhancing local
convection and producing updrafts that maintain dust
aloft. The pluming mechanism is responsible for lofting
dust above the boundary layer thus creating the B storm.
When the radiative effects of airborne dust are excluded
from the simulation, dust does not plume up above the
boundary layer and the B storm never develops. Now
that we have identified the pluming mechanism in the
simulation, we intend to revisit the MCS data to look for
evidence of dust pluming in the observations.
The hours-long lifespan of a dust layer lofted in a
plume and later advected around the planet as a detached
dust layer, coupled with the dependency of the lofting
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cycle [2]. We are in the process of performing a trajectory analysis on the dust plumes in our simulation and
we will assess the importance of this mechanism for the
evolution of the B storm.
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